Zoom tracking adjusts a camera's focal length continuously, to keep the in-focus state of an image during zoom operation. Zoom tracking is important because we want the subjects always in focus even when we are zooming in or out. In DSC (digital still camera), we want the subjects always in focus in order to shorten the lens moving range while auto focusing. The zoom tracking technique can be implemented using a simple curve traced table-lookup method. We can store several zoom position curves with respect to the in-focus lens position, and move the focus lens position by looking up the position table while moving the zoom lens position. FIG. 1 shows the lens position curve. However, the table-lookup method needs a large system memory, which is often limited in portable devices. Another problem of zoom tracking is that the lens position curve selection gets harder while the zoom lens moves toward the telephoto angle. The de-focusing gradually increases as the zoom lens moves toward the telephoto end.
One zoom tracking method in the prior art is called “Adaptive Zoom Tracking”. This algorithm uses the curve interpolation and estimation techniques. Each curve is divided into the linear and non-linear regions as shown in FIG. 2. Please refer to FIG. 2, in the linear region, the left and right end points are stored in the memory and the rest focus positions are calculated from the two points using the linear interpolation method. In the nonlinear region, the focus position at each zoom position is obtained from the stored curve data.
Curves between the upper and lower bound are estimated as in Equation (1).F(k)=F1(k)−R*Df  (1)where F(k) and F1(k) are the focus position of the estimated and upper bound curves at zoom position k, respectively; R is the curve estimation factor of df/Df, where Df is the difference between focus position of the upper and lower bound curves at the zoom position k, and df is the difference of the focus position between the upper bound and the estimation curve at the same position.
The algorithm initially traces the upper bound curve since the difference between the focus positions of each curve is very small in the linear region; in non-linear region, the curve estimation factor is calculated. Finally, zoom curve interpolation and estimation are performed using the curve estimation method.
However, the adaptive zoom tracking mentioned above only traces the upper bound curve, where the loss of steps will get larger while the curve is closer to the lower bound.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop a wireless mouse according to the present invention through wholehearted experience and research.